It depends on your heat load, most refigerators are not charged and tuned to handle the heat load's that most reefkeepers need.
This can lead to stress on the compressor and or poor performance.
The condensor on the back of the refigerator is passive, put a big fan on it if you try this out. It should help quite a bit :P
*edit* I just re-read and saw mention of this being a TEC frig... improving perfomance will be a pain
I have some ideas though :P